Tunable solid-state fluorescence of charge-transfer cocrystal self-assembled by (E)-N’-(9-phenanthrylmethylene) benzohydrazide with TCNB: Stacking mode and theoretical analysis

A CT cocrystal FPTC of donor FPHD and acceptor TCNB was formed via self-assembly. • Donor-acceptor stacking mode and π⋯π interactions were quantified by SCXRD. • CT effect was analyzed through detailed DFT calculation. • Band-gap and optical modulation were induced by CT via the incorporation of TCNB. Investigation of the structure and optical property of charge transfer (CT) cocrystals comprising electron donors and acceptors is indispensable to clarify intrinsic relationships between donors and acceptors and construct new organic fluorescent materials. Herein, the electron donor ( E )-N’-(9-phenanthrylmethylene) benzohydrazide (FPHD), and acceptor 1,2,4,5-benzenetetracarbonitrile (TCNB) formed cocrystal FPTC (FPHD-TCNB) through supramolecular self-assembly. The crystal structure and π⋯π stacking mode of cocrystal FPTC were identified through single-crystal X-ray diffraction. The variation of C ≡ N stretch wavenumbers of TCNB and FPTC in Fourier-transform infrared spectra and the 75 nm red-shift in solid-state ultraviolet visible diffuse reflectance spectra confirmed the formation of cocrystal FPTC. Additionally, the 119 nm red-shift in solid-state fluorescence emission spectra indicated enhanced fluorescence, prolonged average fluorescence lifetime and elevated quantum yield of cocrystal FPTC. Through density functional theory (DFT), the weak interactions in cocrystal FPTC were analyzed, confirming the CT effect in FPTC. Furthermore, the narrowed band gap due to CT effect resulted in the change of transition dipole moment under excited state in cocrystal FPTC, directly leading to improved optical property of FPTC. This study illustrated CT effect on the structure and optical property of cocrystal FPTC via experimental exploration and theoretical analysis, providing a new strategy for novel organic fluorescent materials and endowing the cocrystal with promising research value for optoelectronic applications. Download: Download high-res image (235KB) Download: Download full-size image